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  1. ICF-SW7600

ICF-SW7600 section

[ICF-SW7600 pic] [ICF-SW7600 pic]
ICF-SW7600 (mine, RNW [1])

General information

Pros

  1. Low noise, good sensitivity (comparable to SW7600G, even a bit better on the low bands)
  2. Good selectivity
  3. Unlike the predecessor, it features a stand on the back, a rather sturdy one at that. This was taken over into all the newer models.
  4. Good frequency stability (no LO pulling) even on the high bands
  5. This receiver has always been a bit underrated, so you can often get one fairly cheap (some price range as the predecessor)

Cons

  1. The receiver is not infrequently affected by electrolytic capacitor related failures, which require very good to excellent soldering skills to fix.
  2. Antenna tends to getting loose (screw) – otherwise it seems to be holding up well though
  3. 5 kHz steps are a bit coarse, especially for tuning in SSB stations
  4. While SSB operation is improved vs. the predecessor (e.g. BFO shift to prefer USB or LSB), the bandwidth still is rather wide and the product detector, as in most portables save for Sony's newer ones, is not sideband selective.
  5. Modest FM strong-signal handling and sensitivity (while it was the first to offer FM stereo and does not use a lot of power on this band, it does less well than the predecessor in terms of raw reception and can't keep up with the successor either) – consider FM a nice add-on.

Reviews

  1. Kurztest aus dem ADDX-KURIER
  2. Radio Netherlands' ICF-SW7600 review and listing of older "7600" models - another of those articles that were lost during their 2004 site revamp and consequently did not make it to the Medium Wave Circle's archive. Here's a fresh 1998-vintage copy (*cough* Some bit cobwebs, anyone?) that still found itself on my harddrive. Back in those days, saving a web page with images still was a non-trivial task that required some editing to get the URLs right, as no browser had a function to do that automagically yet.
  3. A review by yours truly (has audio noise spectra illustrating filtering action, check it out!)

Operating manual

Manual downloads at Sony - ICF-SW7600GR, ICF-SW7600G, ICF-SW7600, ICF-7600D (Seems to be broken, refer to the various Yahoo! groups for copies.)

Failures and Repairs

Service docs

Here's a complete service manual (~5 megs) (local mirror). Another complete, albeit BIG copy of the service manual with the schematic and PCBs in color can be found at the Boat Anchor Manual Archive (mirror). (This one is more useful if you want to determine electrolytic capacitor placement and polarity on the board, plus it has all the electrolytics marked in the parts list.)

If you need a service manual in paper form, there are various sources that sell 'em. I have mentioned a local one in the misc links section.

Capacitor related troubles

Like several other approx. 1985 .. 1993 models (including e.g. ICF-SW1, ICF-PRO70 or, less obviously, ICF-SW55), the ICF-SW7600 has its share of problems with early surface mount electrolytic capacitors. If these fail, reception, audio and other problems may result. Leakage may even damage the PCBs. Problems with these things actually aren't restricted to radios, they also give trouble in camcorders, DATs and other such equipment of the time.

Rumor has it that the caps themselves weren't actually that bad but rather manufacturers soldered them a little hotter than they were specified to take, which their rubber seals didn't find too amusing. The expected result is drying out or leakage. And indeed, bad solder joints seem to be pretty much a non-issue on these Sony sets (except for those that see mechanical stress, typically on headphone or DC power jacks).

It is, however, not always just the capacitors themselves; in case of the one in the DC/DC converter, it's being subjected to significant amounts of RF at 1.85 MHz due to having no bypass cap suitable for high frequencies (an ordinary electrolytic certainly isn't and has high losses), which leads to the capacitor heating up and drying out prematurely. (Interestingly, the ICF-SW55 and ICF-SW77 use the same kind of DC/DC setup (and a very similar one is found in the ICF-2001D/2010) yet are not known for excessive DC/DC failures – but if you ever encounter "motorboating" issues with any of them, you know where to look!)

If you have the skills and feel like it, do a complete recapping, at least as far as the surface mount electrolytics are concerned. (If there are any signs of leakage, clean the board as well.) The set would certainly thank you with many more years of trouble-free operation.

I would like to thank those who have provided feedback over the years, as well as Eckhard Neber for initial DC/DC converter troubleshooting / fixing and Helmut G. Vogel for a free recapping job.

Quick repair guide

(This is for those who don't have the time to wade through all the text, hi.)

The #1 trouble spot in this receiver are the surface mount electrolytic capactors used. Commonly defective ones include C127 (in the DC/DC converter) and C69, but generally any of them (including those around the audio power amp) may be dead and even leaky. If some are affected, the others usually are not far behind.

For repair, I would suggest a workshop capable of fixing PC hardware and such if you can't do it yourself - the set is sufficiently high-tech. (All surface mount!) With the service docs and the notes provided on this page, they should have no trouble repairing the set provided the main board has not been damaged by leaked electrolyte.

Have C127 replaced by a suitable tantalum or ceramic capacitor; if there only is an electrolytic at hand (must be pretty tiny!), have a bypass cap of about 100 nF installed, which is not to say that it would hurt in other cases.
Note that as opposed to the schematic, C69 is a 220 F part.

Range of symptoms

Symptoms indicating dead capacitors may be, sorted by section:

If you ever stumble across a set that cannot keep memory and time backed up during a battery change (normally things will be kept for about half an hour or more), check C126, a 0.018 F (parts list says 0.08 F, tpyo?) double layer capacitor or "goldcap". This does not appear to be a very common failure.

Disassembly guide

The service manual is not too detailed and only shows basic disassembly. Here are some notes on how to proceed (no, this is not entirely trivial):

  1. Remove back as detailed in docs
  2. Lift interior at switch / volume control side and remove from front part, take off clipped-on side panel over switches
  3. On back side of main PCB, find and remove short screw close to the center, which may be covered up by some sticky black tape; this holds the P board
  4. Unclip speaker, take a look at wire routing (again, wire may be found under tape), put it to the side
  5. Unclip P board from frame on the right-hand side (front view, normal operating orientation with speaker on left)
  6. Unlock flexible ribbon cable connector on main board; this is two-part, and pushing up the upper one (be careful!) releases the cable; do not lose said upper part!
  7. Remove P board
  8. Unsolder ferrite antenna wires, colors are marked on the PCB (this unfortunately is unavoidable when swapping caps on the main board)
  9. You should now be able to remove the main board from the mounting frame.
  10. For accessing C127, the DC/DC converter shielding (located next to the cutout for the batteries) must be unsoldered on both sides.

This kind of repair requires a fine-tipped soldering iron (preferably a temperature controlled soldering station), a steady hand and good sight. Experience with surface mount parts is recommended. A scope may be useful in problem diagnosis.

DC/DC converter repair notes

The DC/DC converter is a relatively critical component, as it is used to generate a voltage higher than supply (14V) which in turn finds use in tuning voltage generation for both the 1st LO (PLL VCO) and 2nd LO (some fine tuning by means of varicap diode). It is supplied from regulated +3V, which otherwise is used for various components (CX20111 FM/AM RF/IF/Det, LA3335M stereo demodulator, active PLL loop filter, active audio filter).

Both of the usual suspects among dead electrolytics are used for +3V buffering.
C127 is on the primary side of the DC/DC converter, after a choke that's used for blocking RF that might creep back into the supply. Unfortunately for the poor cap, there is no bypass capacitor for it that would work better at high frequencies (the converter itself works at 1.85 MHz), thus keeping most of the high-frequency voltage ripple away. Instead, C127, which has pretty high losses at that kind of frequency, has to endure all the ripple by itself, thus getting heated up and ultimately drying out prematurely.
C69 is situated near the CX20111. It's probably "just" unreliable. This must not be too large or it will interfere with the battery compartment to PCB contacts. (C68 on the ripple filter input may also be worth changing.)

In the ICF-SW7600 that I own, C127 was replaced in 2004 when I found myself someone with better soldering skills. (My attempts with 0805 parts more recently qualify as modern art at most - and that was with a suitable microscope.) A 22F ceramic chip capacitor (then a brand new evaluation sample) was installed, with 100nF of bypass (also a ceramic) in parallel. This is probably a "better than new" solution - a 22F tantalum or ceramic cap only should generally also do just fine.

(Incidentally, when the left output channel ultimately decided to stop working a few years later, the set had the remaining surface mount electrolytics replaced in early 2009. The old ones were checked with a capmeter during the process, they didn't measure up very well any more.)

Audio amplifier cap notes

If power-on pop noise occurs, the primary suspect is C114, which connects to an amplifier pin for pop noise suppression. (Some pop noise under reduced voltages is normal though.)

In case of low audio levels, I would turn my attention to C113 and C116.

Reader input and historical notes

Someone whose ICF-SW7600 was badly affected from bad caps is R. W. Hollander in the Netherlands who wrote:

After two years of bad operation of my Sony ICF-SW7600 it turned out that 65% of the electrolytic capacitors were leaking so much that the PCB around these capacitors became conducting. Resistances of only several kOhm has been found when probe tips were about a millimeter apart on the PCB. This caused wrong voltages on the varicaps (in series with 100kOhm!) and the PLL output voltage (LPF) pulled up to the upper limit. At first, not knowing what the real cause was, I replaced the varicaps of the FM-section (Sony was so kind to supply me two for free), which helped for some months (because I cleaned the PCB as well). Then I only cleaned the area around the varicaps, which also helped. Finally, when I realized the leakage, I replaced all (23) electrolytic capacitors (except the one in the 14V DC-DC) converter in the shielded box). This seems to work! No bad FM-reception and unstable tuning anymore. This repair may easily damage your PCB. Do not try to unsolder the electrolytic capacitors, just crunch the capacitors so that you can unsolder the leads individually.

FM reception range limited or FM not working at all, AM normal

Regarding specifically the FM failure problem, read on what Ben McGee from "down under" told me:

I just bought an ICF-SW7600 at a "swap meet" for A$20. A fine radio on LW/MW/SW, really good!
Naturally, the FM section wasn't working.

I found there was about 50mV of "ripple' (about 50KHZ) on the 3VDC line and no output from the FM VCO on the CX20111 chip.
The ripple seems to be coming from the DC-DC converter supplying 14 V for the varicap diodes. But it's coming out at the 3VDC INPUT to the converter. Varicap tuning voltage was high (14V) due to no VCO output.

I replaced the electrolytic capacitor on pin 23 of CX20111. It's actually 220MFD 4V (the manual says 22MFD [Ed. note: the part list states the correct value for C69, the schematic doesn't]) and the ripple is gone. Initial tests were encouraging, showing the varicap tuning voltage was about 8VDC (I had played with T10 tuning inductor).

I think this is the fix!

[...]

Regards to all, Ben McGee, VK2YEO, Sydney Australia.

And indeed, changing C69 turned out to be the solution to the "no FM" problem. However, you must not choose a capacitor that is physically too large, since then the battery-to-circuitboard contacts may no longer make proper contact. In this case this caused all components to look like they had the full +6VDC on them, normally a very unhealthy condition. But as the saying goes, all is well that ends well, and now Ben's SW7600 is working just fine! :)

Be warned, however, that getting to C69 in the first place is a non-trivial task. You need to take out the speaker (easy), unclip the computer PCB and loosen the interconnecting ribbon cable (fussy) before you even have a chance to get the main PCB off the chassis. Beware of the rod antenna wires, you may want to unsolder them (their positions can be seen in the service manual).

It may be worth noting that the ICF-SW7600G does not use an equivalent cap to C69 (apparently the CXA1376 supply voltage is buffered only by a small 1F ceramic cap), while the SW7600GR does (the 100F 10 V electrolytic C221 in parallel to 1F C220).

With the next problem (below) being solved, I suspect that the "C69 problem" is in fact a combination of a weakened C69 with an underperforming DC/DC converter due to C127 aging. The CX20111 runs off the same voltage that the DC/DC converter is being supplied with and can apparently drag down the voltage far enough to cause trouble if C69 is dead.

Wear and tear

Fred Hopengarten K1VR writes:

I have a Sony ICF-SW7600, S/N 184668, black plastic cover, made for the American market. It has served me well for many years, until 2004 when I suffered two failures. I thought your readers would be interested in the two failures and the solutions.

AC Power Intermittent

Symptom:
The radio works with batteries, but is intermittently on and off when using the "wall wart" power supply (AC power adapter).

Cure:
The problem is that the coaxial power plug has gone in and out many times over the years and loosened the jack. Insert a jewler's screwdriver from the outside of the radio (do not take the radio apart) and, using a flashlight, push the steel spring fingers toward the center of the hole, to make a tighter fit.

UP and BAND Buttons No Longer Work

Symptom:
The radio tunes down, but will not tune up in frequency. Also, it is impossible to go up (or down) band-by-band (skipping the frequencies in-between standard shortwave broadcast allocations).

Cure:
Open up the radio and soak the Tact switch with contact cleaner or almost pure isopropyl alcohol while pushing on switch repeatedly. Watch the switch get "better" by using an ohmmeter across the contacts. Ignore the "open" measurement, which could be 1-9 Megohms (a function of the circuitry behind the switch). Keep cleaning and pressing until the "closed" measurement goes down to less than one ohm (which means you are now measuring the resistance of the VOM probe wires, not the resistance of the switch). The problem is that the most common buttons have worn out the contacts in the Tact switches. Perhaps there is a layer of oxide that has developed with repeated use. I used 99.9 percent pur isopropyl alcohol from a radio parts supplier. If this happens again, replacement switches are available from MCM, Centerville, OH (www.mcmelectronics.com) for USD $0.21 each (quantity 1-9), but you must figure out what is the correct shaft length. I have not, but I think it is part # 28-4723 (0.8 mm), or 28-4725 (1.5 mm), as the next sizes (3.5 mm and 6.0 mm) seem much too tall.

Other problems

No sound

If you don't get any audio from the speaker, there are three things that might be at fault:

Additional information

Tape recorder compatibility

The remote switching capability can be used at least on the following Sony tape recorders:

These tapes apparently have 2.5 mm jacks for this function, so a mechanical adapter is required.

Specified power consumption

Total current spec from the schematic (with minimum output, I suppose):

In this department, the ICF-SW7600 seems to be a nice improvement over the predecessors. So you'd better not be fooled by the lower specified battery life.

The front end

Apparently the ICF-SW7600 introduced the kind of AM front end still used in the ICF-SW7600GR today - 2SK508-K51 as RF amp (source follower) plus a dual balanced mixer with two more FETs of the same type. AGC distribution is, however, a little different from later models.

Tuning step trickery

Seemingly the ICF-SW7600 was the first receiver (save for possibly the diminutive ICF-SW1) to implement a little trick that allows tuning steps half as large as the PLL used for the 1st LO will allow. Apparently the PD1715 only allows 10 kHz steps if LO frequencies of up to a good 85 MHz are desired (6 kHz towards 56 MHz), so they had to get inventive to provide 5 kHz (3 kHz) steps at least.

The classic way of solving such a problem is providing a synthesized 2nd LO with finer tuning steps, as it was done in the ICF-2001 for example (1st IF 66.3 .. 66.4 MHz, then tuned with 1 kHz steps). Now this means a considerable effort, and neither the space nor the budget or power required were available in this case, besides overall phase noise doesn't exactly get better.

Now even in the predecessor, the 2nd LO had already been variable for fine tuning purposes, with a varicap diode pulling the crystal resonator's frequency a bit. This was expanded to include two trimmer resistors and accompanying switching thyristors which (being part of a voltage divider) drop diode tuning voltage when activated by their respective data output lines on the PD1715, thus shifting 2nd LO frequency downwards and accordingly reception frequency upwards. It is clear that this requires alignment and may not give the ultimate precision - in fact, on my sample, AM carrier hets vary a little in frequency between "0" and "5" positions (maybe 200..300 Hz, no more). (The 1st IF filter also needs to be wide enough for a 5 kHz shift to not matter much, but on 55.845 MHz that's usually the case anyway, think ~30 kHz of bandwidth.) Kinda neat, isn't it?

Knowing this, it is no longer all that surprising that "0" and "5" positions behave differently in case of DC/DC converter (electrolytic) troubles, and that a shift in actual reception frequency (caused by the 2nd LO being off due to too low a varicap tuning voltage) is commonly encountered then.

Other sets pulling the same stunt include Grundig YB400(PE), Degen DE1103 (including Eton / Lextronix E5) and Redsun RP2000/2100, this time for 1 kHz steps. That none of them is known for exceptional phase noise performance (apparently phase noise can vary strongly from sample to sample on the Grundig, a test with an early-model DE1103 yielded disappointing results of barely 13 dB SNR even under excellent conditions, only the Redsun yields some 25 dB at least as long as you turn down the RF gain with strong signals) may or may not be coincidence (they all use Sanyo PLL chips, too).

This can be taken even further, by the way. If you use a multi-bit D/A converter connected to the main PLL synthesizer (or microprocessor) instead of only a single-bit output, not only one intermediate step is possible but a whole bunch. This is where sets like ICF-SW55, ICF-SW100 and ICF-SW07 get their 100 Hz steps from! (Hmm, and all of these are known to exhibit some warbling on SSB... The SW7600, provided it has a properly working DC/DC converter, is stable as a rock, save for a bit of thermal drift.) The Sangean ATS-909 even generates 40 Hz steps (PWM output followed by higher-order filtering instead of multi-bit DAC, which basically does the same with only a single data line).

Links

Yahoo! Groups:

Radio Netherlands' measurements

Sensitivity
Frequency Range Sensitivity (in microvolts)
for 20 dB S+N/N
 2 -  6 MHz 2.1 µV
12 - 17 MHz 10.6 µV
Real-world ("dynamic") selectivity
Distance Suppression
+/-  5 kHz 26.0 dB
+/- 10 kHz 46.0 dB
+/- 15 kHz 51.0 dB
Misc.
Blocking level 4.2 mV
Image Rejection
(at +/- 910 kHz)
16 dB
Intercept Point -5 dBm

Image rejection just 16 dB?! Hmm, as far as the limited function of my own SW7600 allowed I could not find any significant difference in image rejection vs. the 7600G, and that certainly is better than 16 dB.

Next: ICF-7601, ICF-7600DA/ICF-7700

Quick links

Write to the author (Stephan Großklaß, "Grossklass" in 7 bit)!

Created 1999-06-01 (yyyy-mm-dd)
Last revision 2011-05-18